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          java的equals引发的血案
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            <div class="post-description">使用 == 对 Integer 进行数值判断导致的bug</div>

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        <p>记一次 .equals 引起的bug</p>
<h4 id="76-最小覆盖子串"><a href="#76-最小覆盖子串" class="headerlink" title="76. 最小覆盖子串"></a><a target="_blank" rel="noopener" href="https://leetcode-cn.com/problems/minimum-window-substring/">76. 最小覆盖子串</a></h4><p>难度困难1356</p>
<p>给你一个字符串 <code>s</code> 、一个字符串 <code>t</code> 。返回 <code>s</code> 中涵盖 <code>t</code> 所有字符的最小子串。如果 <code>s</code> 中不存在涵盖 <code>t</code> 所有字符的子串，则返回空字符串 <code>&quot;&quot;</code> 。</p>
<p><strong>注意：</strong></p>
<ul>
<li>对于 <code>t</code> 中重复字符，我们寻找的子字符串中该字符数量必须不少于 <code>t</code> 中该字符数量。</li>
<li>如果 <code>s</code> 中存在这样的子串，我们保证它是唯一的答案。</li>
</ul>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line">public class Solution&#123;</span><br><span class="line">    public String minWindow(String s, String t) &#123;</span><br><span class="line">        Map&lt;Character, Integer&gt; window = new HashMap&lt;&gt;();</span><br><span class="line">        Map&lt;Character, Integer&gt; need = new HashMap&lt;&gt;();</span><br><span class="line">        int valid = 0;</span><br><span class="line">        int left=0,right=0;</span><br><span class="line">        int start = 0,len = Integer.MAX_VALUE;</span><br><span class="line"></span><br><span class="line">        for(char c : t.toCharArray())&#123;</span><br><span class="line">            need.put(c, need.getOrDefault(c, 0)+1);</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        while(right &lt; s.length()) &#123;</span><br><span class="line">            char c = s.charAt(right);</span><br><span class="line">            right++;</span><br><span class="line">            window.put(c, window.getOrDefault(c, 0)+1);</span><br><span class="line">            if(need.containsKey(c))&#123;</span><br><span class="line">            // 这里如果使用 == 判断，则会出错</span><br><span class="line">                if(need.get(c).equals(window.get(c)))&#123;</span><br><span class="line">                    valid++;</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line"></span><br><span class="line">            while(valid == need.size())&#123;</span><br><span class="line">                if(right -left &lt; len)&#123;</span><br><span class="line">                    start = left;</span><br><span class="line">                    len = right - left;</span><br><span class="line">                &#125;</span><br><span class="line">                char d = s.charAt(left);</span><br><span class="line">                left++;</span><br><span class="line">                if(need.containsKey(d))&#123;</span><br><span class="line">                // 这里如果使用 == 判断，则会出错</span><br><span class="line">                    if(window.get(d).equals(need.get(d)))&#123;</span><br><span class="line">                        valid--;</span><br><span class="line">                    &#125;</span><br><span class="line">                &#125;</span><br><span class="line">                window.put(d, window.get(d) - 1);</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        return len == Integer.MAX_VALUE ? &quot;&quot; : s.substring(start, start+len);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>



<p>在s和t为超大的字符串的 时候，存放在map中的Integer 已经超过128的范围，这时候，就回 new 出新的对象，这时候使用== 判断，则会不一样。导致测试用例不能通过。</p>

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